Methods have been described where acrylic acid (AA) is produced via the pyrolysis of polypropiolactone (PPL) (e.g., see U.S. Pat. No. 2,361,036). However, PPL pyrolysis as described in this and related literature does not produce acrylic acid of sufficient purity for direct use in radical polymerization for superabsorbent polymer (SAP) production. Instead, the methods require expensive and energy intensive purification of the acrylic acid before it can be polymerized to produce SAP. There is therefore a need in the art for methods of directly producing glacial acrylic without the need for expensive and energy intensive AA purification.
The pyrolysis of PPL to acrylic acid (AA) presents several challenges for commercialization.

In the above scheme, each * indicates a point of attachment on either side of monomeric units of the PPL polymer. The pyrolysis of PPL to crude or glacial acrylic acid is beset with problems. Although PPL can be prepared from BPL, this conversion may proceed with relatively little control, from batch to batch, in regards to the molecular weight and/or polydispersity of the PPL.
Polymerization inhibitors and anti-foaming agents may be added, to the PPL during pyrolysis, or to acrylic acid once formed, to control reactivity, preserve acrylic acid from degradation, polymerization and/or reduce foaming. However, there is a growing need to produce acrylic acid, particularly glacial acrylic acid, having little or no impurities, and low levels of polymerization inhibitors and/or anti-foaming agents, in order to minimize contamination of downstream polymers, such as SAPs, and end product articles such as diapers.